Financial Instruments Owned, at Fair Value and Financial Instruments Sold, But Not Yet Purchased, at Fair Value - Financial Instruments Owned and Financial Instruments Sold, But Not Yet Purchased (Detail) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial instruments owned, at fair value	$ 292,420	$ 293,940
Financial instruments sold, but not yet purchased, at fair value	115,154	115,248
Cash Instruments Assets [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial instruments owned, at fair value	230,817	232,293
Investments in funds at NAV	6,859	7,757
Subtotal	237,676	240,050
Cash Instruments Assets [Member] | Commercial Paper, Certificates of Deposit, Time Deposits and Other Money Market Instruments [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial instruments owned, at fair value	2,463	2,583
Cash Instruments Assets [Member] | U.S. Government and Federal Agency Obligations [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial instruments owned, at fair value	45,306	46,382
Cash Instruments Assets [Member] | Non-U.S. Government and Agency Obligations [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial instruments owned, at fair value	38,036	31,772
Cash Instruments Assets [Member] | Loans and Securities Backed by Commercial Real Estate [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial instruments owned, at fair value	4,523	4,975
Cash Instruments Assets [Member] | Loans and Securities Backed by Residential Real Estate [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial instruments owned, at fair value	9,411	13,183
Cash Instruments Assets [Member] | Bank Loans and Bridge Loans [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial instruments owned, at fair value	9,859	12,164
Cash Instruments Assets [Member] | Corporate Debt Securities [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial instruments owned, at fair value	21,128	16,640
Cash Instruments Assets [Member] | State and Municipal Obligations [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial instruments owned, at fair value	1,705	992
Cash Instruments Assets [Member] | Other Debt Obligations [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial instruments owned, at fair value	1,163	1,595
Cash Instruments Assets [Member] | Equities and Convertible Debentures [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial instruments owned, at fair value	91,280	98,072
Cash Instruments Assets [Member] | Commodities [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial instruments owned, at fair value	5,943	3,935
Cash Instruments Liabilities [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial instruments sold, but not yet purchased, at fair value	70,715	68,477
Cash Instruments Liabilities [Member] | U.S. Government and Federal Agency Obligations [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial instruments sold, but not yet purchased, at fair value	14,751	15,516
Cash Instruments Liabilities [Member] | Non-U.S. Government and Agency Obligations [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial instruments sold, but not yet purchased, at fair value	19,589	14,973
Cash Instruments Liabilities [Member] | Loans and Securities Backed by Commercial Real Estate [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial instruments sold, but not yet purchased, at fair value	6	4
Cash Instruments Liabilities [Member] | Loans and Securities Backed by Residential Real Estate [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial instruments sold, but not yet purchased, at fair value		2
Cash Instruments Liabilities [Member] | Bank Loans and Bridge Loans [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial instruments sold, but not yet purchased, at fair value	468	461
Cash Instruments Liabilities [Member] | Corporate Debt Securities [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial instruments sold, but not yet purchased, at fair value	6,313	6,123
Cash Instruments Liabilities [Member] | State and Municipal Obligations [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial instruments sold, but not yet purchased, at fair value		2
Cash Instruments Liabilities [Member] | Other Debt Obligations [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial instruments sold, but not yet purchased, at fair value	2	2
Cash Instruments Liabilities [Member] | Equities and Convertible Debentures [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial instruments sold, but not yet purchased, at fair value	29,586	31,394
Derivatives [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial instruments owned, at fair value	54,744	53,890
Financial instruments sold, but not yet purchased, at fair value	$ 44,439	$ 46,771